Intepreting a two-sided spectrum.

1. The problem statement, all variables and given/known data
In a two-sided spectrum, there's a complex component of 1-j2 at frequency f = -1000Hz. What is the component at 1000Hz and the signal in time plane?

2. Relevant equations

3. The attempt at a solution
So the component at 1000Hz is 1-j2 as well. And the signal in time plane is [itex]a*cos(2000\pi t)[/itex], but what is the amplitude. Is it simply 2*(1-j2)? Is there a possibility to calculate an inverse of the coefficient c_n of the Fourier series?